1. Field of the Invention
The present invention relates to a pump that sucks in and discharges fluid such as oil.
2. Description of Related Art
A vehicle having a start-stop function is generally provided with an electric oil pump. In such a vehicle, while idling is stopped, the required minimum hydraulic pressure is supplied to portions requiring hydraulic pressure by an electric oil pump, instead of a mechanical pump that is driven by an engine. Accordingly, the vehicle can be quickly restarted.
The aforementioned electric oil pump includes an outer rotor, an inner rotor, and a housing. Internal teeth are formed on the inner periphery of the outer rotor. The internal teeth are formed using trochoid curves. External teeth are formed on the outer periphery of the inner rotor. The external teeth are formed using trochoid curves and mesh with the internal teeth. The inner rotor is rotated by a motor. A pump chamber, in which the outer rotor and the inner rotor are rotatably housed, is defined in the housing.
A suction flow passage and a discharge flow passage, which communicate with the pump chamber, are formed in the housing. A suction-side groove with which the suction flow passage communicates and a discharge-side groove with which the discharge flow passage communicates are formed at an interval in the circumferential direction of the bottom of the pump chamber so as to be recessed in the bottom of the housing. When the inner rotor and the outer rotor of the electric oil pump, which has the above-mentioned configuration, are rotated while meshing with each other, oil sucked from the suction flow passage is discharged from the discharge flow passage.
Japanese Patent Application Publication No. 2008-151065 (JP 2008-151065 A) proposes an electric oil pump including a relief valve that returns oil to a suction-side groove from a discharge-side groove when excessive pressure is applied to a discharge side of a pump chamber.
This electric oil pump may be fitted to bosses protruding from an outer surface portion of a transmission. The relief valve is provided between inner and outer rotors and an outer surface of the transmission. Therefore, the thickness of the electric oil pump is increased by the thickness of the relief valve, and thus, the electric oil pump is not easily fitted to the transmission.